1. Field of the Invention
The present invention relates to an optical coupling circuit for optical communication that allows the light emitted from an optical transmission line such as an optical fiber to be received by a photodetector element, and in particular to an optical coupling circuit that enables both highly efficient coupling as well as low cost.
2. Description of the Related Art
An optical coupling circuit for optical communication that allows the output light of an optical transmission line such as an optical fiber to be received at a photodetector element is a key component in the configuration of an optical communication system.
In the interest of reducing the costs of optical communication devices, there has been a growing demand in recent years for optical coupling circuits that feature easy assembly and efficient optical incidence.
As one example of an optical coupling circuit that can meet this demand, an optical coupling circuit has been proposed that raises the efficiency of light incidence to a photodetector element by forming a lens at the emission end surface of an optical fiber so as to reduce the spread of light emitted from the optical fiber and thereby allow the photodetector element to efficiently receive light emitted from the optical fiber.
Nevertheless, this example of the prior art has several drawbacks. First, due to the extremely small outer diameter of approximately 125 .mu.m of an optical fiber as well as the small diameter of approximately 50 .mu.m of the lens, the fabrication process for forming the lens on the end surface of the optical fiber is complex and entails numerous fabrication steps.
In addition, the high-precision processing techniques that are required in forming such lenses on the emission end surfaces of optical fibers results in poor product yield of the fabrication process.
Finally, there is the problem that the small dimensions of the lens necessitate sophisticated inspection equipment for monitoring the products. These problems all contribute to the difficulty of reducing the cost of an optical coupling circuit.